The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A typical modern multiple speed automatic transmission includes a plurality of planetary gear assemblies and selectively engaged friction clutches and friction brakes that achieve a plurality of forward speeds or gear ratios and reverse.
Increasingly demanding economic, performance and efficiency goals continue to encourage automatic transmission research and development. A result of this effort has been a steady increase in the number of available forward speeds or gear ratios in an automatic transmission.
In such transmissions, the elements of a plurality of planetary gear assemblies are (1) connected by permanent coupling members, (2) selectively connected by friction clutches or (3) selectively grounded by friction brakes. Specific combinations of the clutches and brakes are engaged or activated in sequence to provide a predetermined sequence of numerically related gear ratios and thus output speeds and torques.
While such transmissions closely match the power and torque outputs of an engine to the vehicle speed and load, six, seven, eight and nine speed automatic transmissions are known to have drawbacks. Two known and related drawbacks are complexity and cost. A corollary to such complexity is frictional loss. Each of the torque transmitting devices, namely, the clutches and brakes, contributes to frictional losses, referred to as spin losses, when they are not engaged. Three primary factors influence overall transmission spin losses: the total number of clutches and brakes, the size or torque capacity of the clutch or brake and the instantaneous speed difference between the input and output of the clutch or brake.
The present invention provides an automatic transmission having nine forward speeds or gear ratios and reverse which exhibits reduced frictional losses.